Incomplete Dominance

There are exceptions to the dominant-recessive pattern. Incomplete dominance occurs when two different alleles control a characteristic but neither is dominant. Instead the different alleles of some genes can be expressed in the heterozygous condition to produce an intermediate phenotype.

For example: snapdragon colour

R = red; r = white P = red x white (RR x rr) F1: genotype = 100% Rr F1: phenotype = 100 % pink F1 r R Rr

F2: genotype = 25% RR, 50% Rr, 25% rr F2 = Rr x Rr F2: genotype = 25% RR, 50% Rr, 25% rr F2: phenotype = 25% red, 50% pink, 25% white F2 R r RR Rr rr

What colour flowers would result from the following crosses? a) red flower x pink flower b) white flower x pink flower c) red flower x white flower d) pink flower x pink flower

Answers: a) 50% red and 50% pink b) 50% white and 50% pink c) 100% pink d) 25% red, 50% pink, 25% white